Depends. Ovulation typically takes place 14 days prior to the menstrual cycle. Therefore, in a 28 day cycle, ovulation usually happens at approximately day 14. In women who have cycles greater than 28 days, ovulation will take place later than day 14. In women with cycles shorter than 28 days, ovulation will take place earlier than day 14.
Day 14 but it varies. In an idealized 28-day cycle ovulation occurs 14 days after the first day (cd 14) of the last mentrual period. In real life, most of us have seen apparently normal ovulations between day 11 and maybe 15-16. For women with regular but longer cycles, let's use 35 days as an example, best guess is usually 35-14= cycle-day 21. With irregular cycles, there is no general reliable rule of thumb.